1. Field of the Invention
This invention relates, generally, to strain relief devices. More particularly, it relates to a strain relief device for power cords.
2. Description of the Prior Art
Many users of electrical equipment pull on the cord instead of the plug when they are in a hurry to unplug the device. Most plugs include strain relief protection and the plug will withdraw from the socket before the electrical conductors that are sheathed within the power cord will separate from their protective terminals.
However, the power cord for most tools and appliances is permanently connected to the tool or appliance at the end of the power cord opposite from the plug. Many tools and appliances have nominal strain relief protection at that end of the power cord. However, in many work places, including manufacturing or assembly facilities, workers routinely pull on such cords at the tool or appliance end in order to move the tool or appliance nearer to themselves. Over time, the strain relief protection degrades and the electrical conductors sheathed within the power cord are pulled from their respective electrical terminals.
One well-known strain relief device is an elongate coiled spring, typically formed of a relatively hard plastic. A plastic cap is attached by a living hinge to a preselected end of the coiled spring. A rigid thin plastic plate is integrally formed with the cap. The power cord is passed through the lumen of the coiled spring, and the cap is closed. This causes the thin plate to tightly pinch the cord, thereby providing at least some strain relief protection when a user pulls on the cord.
However, a strong pull on the cord will overcome the pinching action of the rigid thin plate because the plate is thin. This concentrates the pinching action without spreading it out over a large area. The strain relief may fail in two ways. First, the pinching action may slip, allowing the rubberized power cord and the electrical conductors sheathed therewithin to withdraw from the tool or appliance. In a second type of failure, the pinching action maintains the rubberized sheath of the power cord in place while the pulling action results in travel of the electrical conductors relative to said stationary sheath. The conductors thus separate from their respective electrical terminals, thereby defeating the protective device even though the rubberized sheath of the power cord has not moved.
Some conventional strain relief devices actually grip the cord, but do so by tightening the cord from within. However, such tightening does not prevent the cord from being pulled out.
Conventional strain relief devices also have abrupt, sharp ends that allow the cord to bend ninety degrees)(90°, leading to eventual breaking.
Several different types of conventional strain relief devices may be seen at heyco.com.
There is a need, therefore, for a strain relief protective device that does not rely upon a concentrated pinching action to provide strain relief.
There is also a need for an improved strain relief device that does not reply upon tightening the cord from within.
A need further exists for a strain relief device that increases its strength as the cord is pulled harder.
There is also a need for a strain relief device that protects a power cord at the point of exit of the power cord from the strain relief device.
However, in view of the prior art considered as a whole at the time the present invention was made, it was not obvious to those of ordinary skill in this field how an improved strain relief protective device could be provided.